// Copyright 2011 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef V8_DIY_FP_H_
#define V8_DIY_FP_H_

#include <stdint.h>

#include "src/base/logging.h"
#include "src/base/macros.h"

namespace v8 {
namespace internal {

    // This "Do It Yourself Floating Point" class implements a floating-point number
    // with a uint64 significand and an int exponent. Normalized DiyFp numbers will
    // have the most significant bit of the significand set.
    // Multiplication and Subtraction do not normalize their results.
    // DiyFp are not designed to contain special doubles (NaN and Infinity).
    class DiyFp {
    public:
        static const int kSignificandSize = 64;

        DiyFp()
            : f_(0)
            , e_(0)
        {
        }
        DiyFp(uint64_t f, int e)
            : f_(f)
            , e_(e)
        {
        }

        // this = this - other.
        // The exponents of both numbers must be the same and the significand of this
        // must be bigger than the significand of other.
        // The result will not be normalized.
        void Subtract(const DiyFp& other)
        {
            DCHECK(e_ == other.e_);
            DCHECK(f_ >= other.f_);
            f_ -= other.f_;
        }

        // Returns a - b.
        // The exponents of both numbers must be the same and this must be bigger
        // than other. The result will not be normalized.
        static DiyFp Minus(const DiyFp& a, const DiyFp& b)
        {
            DiyFp result = a;
            result.Subtract(b);
            return result;
        }

        // this = this * other.
        V8_EXPORT_PRIVATE void Multiply(const DiyFp& other);

        // returns a * b;
        static DiyFp Times(const DiyFp& a, const DiyFp& b)
        {
            DiyFp result = a;
            result.Multiply(b);
            return result;
        }

        void Normalize()
        {
            DCHECK_NE(f_, 0);
            uint64_t f = f_;
            int e = e_;

            // This method is mainly called for normalizing boundaries. In general
            // boundaries need to be shifted by 10 bits. We thus optimize for this case.
            const uint64_t k10MSBits = static_cast<uint64_t>(0x3FF) << 54;
            while ((f & k10MSBits) == 0) {
                f <<= 10;
                e -= 10;
            }
            while ((f & kUint64MSB) == 0) {
                f <<= 1;
                e--;
            }
            f_ = f;
            e_ = e;
        }

        static DiyFp Normalize(const DiyFp& a)
        {
            DiyFp result = a;
            result.Normalize();
            return result;
        }

        uint64_t f() const { return f_; }
        int e() const { return e_; }

        void set_f(uint64_t new_value) { f_ = new_value; }
        void set_e(int new_value) { e_ = new_value; }

    private:
        static const uint64_t kUint64MSB = static_cast<uint64_t>(1) << 63;

        uint64_t f_;
        int e_;
    };

} // namespace internal
} // namespace v8

#endif // V8_DIY_FP_H_
